No artists I know are able to go into their studios and instantly produce art on demand. There is usually a period of time in which they resort to various tactics to jump start their creativity. This can be something as simple as sweeping out the place, or a more inner directed practice like meditation. Only then can they begin the serious business of making art.
I'm a lifelong doodler, a trait that's gotten me bounced from more than one menial job. Nonetheless, early on, I realized the importance of this seemingly innocent habit, and now use doodling to first get going in the studio. I often begin the creative day doing quick gestural drawings for an hour or so, after which time the ground has been prepared for more imposing work to come. I call this exercise "warm-ups," and above is one I completed this morning.